Benzidine derivatives and electrophotosensitive material using the same

Abstract: The present invention relates to a benzidine derivative represented by the general formula (1): wherein R¹ to R⁶, m and n are as defined in the present specification. The benzidine derivative improves durability and heat resistance of a membrane containing the same while maintaining high hole transferring capability. Therefore, an electrophotosensitive material, which comprises a photosensitive layer containing the benzidine derivative, has high sensitivity and is superior in durability and heat resistance.

Description: BACKGROUND OF THE INVENTION The present invention relates to novel benzidine derivatives which are suitably used as charge transferring materials, particularly hole transferring materials in applications such as solar batteries, electroluminescent devices, electrophotosensitive materials and the like, and electrophotosensitive materials using the same. As charge transferring materials, there have been known various organic compounds such as carbazole compounds, oxadiazole compounds, pyrazoline compounds, hydrazone compounds, stilbene compounds, phenylenediamine compounds, benzidine compounds and the like. These charge transferring materials are normally used in a state where they are dispersed in a membrane of a suitable binding resin. In case of the electrophotosensitive material, for example, so-called organic photosensitive materials (OPC) such as single-layer type electrophotosensitive materials comprising a single-layer type photosensitive layer wherein the above charge transferring material and a charge generating material which generates a charge due to light irradiation are dispersed in a binding resin, multi-layer type electrophotosensitive materials comprising a charge transferring layer containing the above electric transferring material and a charge generating layer containing a charge generating material, etc. are normally used. Such an organic photosensitive materials have an advantage that they are superior in processability and can be easily produced, and which offers a great degree of freedom for design of performance. Among these compounds, there can be suitably used a 3,3'-dimethylbenzidine derivative represented by the formula: wherein R a , R b , R c and R d are same or different and indicate a hydrogen atom, a lower alkyl group, a lower alkoxy group or a chlorine atom, which belongs to the benzidine derivative, because of its high hole transferring capability and good compatibility with the binding resin (see JP-A-5-210099). However, the above 3,3'-dimethylbenzidine derivatives have such a disadvantage that they have generally low melting points (about 180 °C or less) and therefore the glass transition temperature (Tg) of a membrane comprising the 3,3'-dimethylbenzidine derivative dispersed in the binding resin becomes low, which results in deterioration of durability, heat resistance and the like. EP-A-0318916 discloses benzidine derivatives according to the above general formula, in which R a , R b , R c and R d , are hydrogen atoms, lower alkyl groups, lower alkoxy groups, or halogen atoms and the methyl groups of the biphenyl moiety are replaced by any of the atoms or groups just mentioned. Moreover, each of the four outer benzene rings can have up to three substituents as aforesaid and each ring of the biphenyl moiety can have up to two substituents as aforesaid. The benzidene derivatives may be used in the photosensitive layer of an electrophotographic material. US-A-4933245 discloses an electrophotographic photoreceptor having as a charge transport material in a photoconductive layer a benzidine derivative according to the above general formula, in which R a , R b , R c and R d are each a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, an alkoxycartonyl group or a substituted amino group. The methyl groups of the biphenyl moiety are replaced by alkyl groups. The Derwent abstract of JP-A-2-277071 discloses benzidine derivatives according to the above general formula, in which R a and R c are hydrogen atoms, the benzene rings having R b and R d as substituents are replaced by biphenyl groups and each ring of the biphenyl moiety is unsubstituted or substituted at any position by an alkyl or alkoxy group or a halogen atom. The benzidene derivative may be used in a multi-layer electrophotosensitive material. In case of an electrophotosensitive material, for example, the steps of 1 ○ charging of the surface of the electrophotosensitive material due to corona discharge, 2 ○ formation of a electrostatic latent image due to exposure, 3 ○ toner development of the electrostatic latent image due to adhesion of toner, 4 ○ image transfer of the toner image to a paper and 5 ○ removal of the residual toner on the surface of the electrophotosensitive material after image transfer are repeated. For cleaning the residual toner, there can be used a cleaning blade which is pressure-contacted on the surface of the electrophotosensitive material. Therefore, in an electrophotosensitive material using a conventional benzidine derivative, a pressure welding dent is formed at the part where the cleaning blade has been pressure-contacted when the image forming apparatus is stopped, thereby causing various failures of image. Further, when operating the image forming apparatus, the temperature of the interior of the apparatus increases to about 50 °C and therefore a recess is formed on the surface of the electrophotosensitive material, thereby causing various failures of image. SUMMARY OF THE INVENTION The present inventors have striven to increase the melting point of the benzidine derivative, and they carried out molecular designing according to the policy. As a result, it has been found that the melting point of the benzidine derivative can be increased while maintaining high hole transferring capability and good compatability with the binding resin by satisfying at least one of the following conditions, and the present invention has been accomplished. (1) At least two out of four outer phenyl groups of the benzidine derivative are substituted with two or three alkyl groups. (2) Two out of four outer phenyl groups of the benzidine derivative are substituted with straight-chain or branched alkyl groups having 3 to 5 carbon atoms. (3) Phenyl groups are bonded to para-positions of two outer phenyl groups of the benzidine derivative to form biphenyl groups, thereby imparting stretch of space to a π-electron of conjugate system. Benzidine derivatives of the present invention can be superior in compatibility with the binding resin while maintaining high hole transferring capability. The derivatives can also improve the durability, heat resistance, etc. of a membrane formed by dispersing the derivative in a binding resin. The present invention can also provide high-performance electrophotosensitive materials using the above benzidine derivatives as a hole transferring material, the materials can have high sensitivity as well as excellent durability and heat resistance. Benzidine derivatives of the present invention are represented by the following general formulas (1) and (1') and specific formulas (2-a) to (2-f): I. the general formula (1) : wherein R 1 and R 2 are the same or different and indicate a hydrogen atom or a methyl group; R 3 and R 4 indicate a methyl group; R 5 and R 6 are the same or different and indicate an alkyl group having 3 to 5 carbon atoms or a phenyl group which may contain a substituent; and m and n are the same or different and indicate an integer of 2 or 3, preferably the general formula (1'): wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , m and n are as defined above. II. The formulas (2-a) to (2-f): The electrophotosensitive material of one embodiment of the present invention comprises a conductive substrate, and a photosensitive layer provided on the conductive substrate, said photosensitive layer containing at least one of benzidine derivatives represented by the above general formulas (1) and (1') and specific formulas (2-a) to (2-f) as a hole transferring material. BRIEF EXPLANATION OF DRAWINGS Figs. 1 to 6 are graphs illustrating the results of infrared spectroscopic analysis of benzidine derivatives obtained in Synthesis Examples 1, 2, 4, 7, 8 and 11, respectively. DETAILED DESCRIPTION OF THE INVENTION Carbon atom of alkyl groups represented by the substituents R 5 , R 6 , in the above general formulas (1) and (1') are, as described above, limited to 3 to 5 carbon atoms. When the number of the carbon atom of the alkyl group is less than 3, good compatibility with the binding resin can not be obtained. On the other hand, when the number of the carbon atom of the alkyl group exceeds 5, hole transferring capability deteriorates. Examples of the alkyl group having 3 to 5 carbon atoms include straight-chain or branched alkyl groups such as propyl group (n-Pr), isopropyl group (i-Pr), butyl group (n-Bu), isobutyl group (i-Bu), tert-butyl group (t-Bu), pentyl group and the like. Examples of the other alkyl group of which number of the carbon atom is not specifically limited include lower alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, hexyl group and the like. Particularly, methyl and ethyl groups are suitably used. The symbols m and n which define the number of substituents in the general formula (1) are limited to 2 or 3, as described above. When the number of substituents R 3 and R 4 is 1, the melting point of the benzidine derivative can not be improved. Further, when the number of substituents is not less than 4, good compatibility with the binding resin is not obtained. Examples of the substituent with which the phenyl group may be substituted include alkyl group, alkoxy group, halogen atom and the like. Examples of the benzidine derivative represented by the general formula (1) include compounds represented by the following formulas (1-a) to (1-j). The benzidine derivative of the present invention can be synthesized by various methods. For example, the benzidine derivative of the above formula (1-a) can be synthesized according to the following reaction scheme. Firstly, N,N'-diacetyl-3,3'-dimethylbenzidine represented by the following formula (7) and 3,4-dimethyliodobenzene represented by the formula (8) are mixed together with copper powder, copper oxide or copper halide in a molar ratio of 1:2 and the mixture was reacted in the presence of a basic substance to give N,N'-diacetyl-N,N'-bis(3,4-dimethylphenyl)-3,3'-dimethylbenzidine represented by the formula (9). Then, N,N'-diacetyl-N,N'-bis(3,4-dimethylphenyl)-3,3'-dimethylbenzidine represented by the formula (9) is subjected to a deacetylation reaction in the presence of an amide-decomposition catalyst such as acid to give N,N'-bis(3,4-dimethylphenyl)-3,3'-dimethylbenzidine represented by the following formula (10), which is reacted with 4-n-butyliodobenzene in a molar ratio of 1:2 to give a benzidine derivative of the formula (1-a). Further, the benzidine derivative of the present invention can also be synthesized by the following reaction scheme in place of the above synthesis method. The following reaction scheme illustrates a synthesis method of the benzidine derivative of the formula (1-d). Firstly, 4,4'-diiodobiphenyl represented by the following formula (7') and p-isopropylacetanilide represented by the formula (8') are mixed together with copper powder, copper oxide or copper halide in a molar ratio of 1:2 and the mixture was reacted in the presence of a basic substance to give N,N'-diacetyl-N,N'-bis(4-isopropylphenyl)benzidine represented by the formula (9'). Then, N,N'-diacetyl-N,N'-bis(4-isopropylphenyl)benzidine represented by the above formula (9') is subjected to a deacetylation reaction to give N,N'-bis(4-isopropylphenyl)benzidine represented by the following formula (10'), which is reacted with 2,4-dimethyliodobenzene represented by the formula (10) in a molar ratio of 1:2 according to the same manner as that described above to give a benzidine derivative of the formula (1-d). As described above, the benzidine derivative of the present invention is suitably used as a charge transferring material, particularly hole transferring material in applications such as solar battery, electroluminescent material, electrophotosensitive material and the like, and can also be used in other various fields. The electrophotosensitive material of the present invention comprises a photosensitive layer on a conductive substrate, said photosensitive layer containing one or more sorts of benzidine derivatives represented by the above general formulas (1) and (1') and specific formulas (2-a) to (2-f). The photosensitive layer is classified into two types, i.e. a single-layer type photosensitive layer and a multi-layer type photosensitive layer. The constitution of the present invention can be applied to both photosensitive layers. The single-layer type photosensitive layer may be obtained by applying a coating solution, which is prepared by dissolving or dispersing at least one of benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f) as a hole transferring material, a charge generating material and a binding resin in a suitable solvent, on a conductive substrate using a means such as coating, followed by drying. Further, the multi-layer type photosensitive layer may be obtained by forming a charge generating layer containing a charge generating material on a conductive substrate using a means such as deposition or coating, applying a coating solution containing at least one of benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f) and a binding resin on the charge generating layer using a means such as coating, followed by drying to form a charge transferring layer. To the contrary, a charge transferring layer may be formed on a conductive substrate and then a charge generating layer may be formed thereon. Non-limited examples of the charge generating material include powder of inorganic photoconductive materials (e.g. selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, α-silicon, etc), azo pigments, perylene pigments, anthanthrone pigments, phthalocyanine pigments, indigo pigments, triphenylmethane pigments, therene pigments, toluidine pigments, pyrazoline pigments, quinacridon pigments, dithioketopyrrolopyrrole pigments and the like. These charge generating materials can be used alone or in combination thereof according to the range of sensitivity of the electrophotosensitive material. The benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f) as the hole transferring material can be used alone or in combination with the other charge transferring materials which have hitherto been known. Examples of the other charge transferring material include various electron transferring materials and hole transferring materials. Examples of the electron transferring material include electron attractive materials such as diphenoxy compounds, benzoquinone compounds, naphthoquinone compounds, malononitrile, thiopyran compounds, tetracyanoethylene, tetracyanoquinodimethane, chloroanil, bromoanil, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4,7-trinitro-9-dicyanomthylenefluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromomaleic anhydride, etc., high-molecular electron attractive materials and the like. Examples of the hole transferring material include electron donative materials such as nitrogen-containing cyclic compounds and condensed polycyclic compounds which include diamine compounds other than benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f); diazole compounds such as 2,5-bis(4-methylaminophenyl)-1,3,4-oxadiazole, etc.; styryl compounds such as 9-(4-diethylaminostyryl)anthracene, etc.; carbazole compounds such as polyvinyl carbazole, etc.; pyrazoline compounds such as 1-phenyl-3-(p-dimethylaminophenl)pyrazoline, etc.; hydrazone compounds; triphenylamine compounds; indol compounds; oxazole compounds; isooxazole compounds, thiazole compounds; thiadiazole compounds; imidazole compounds; pyrazole compounds; triazole compounds and the like. Further, when using a charge transferring material having film forming properties such as polyvinyl carbazole, the binding resin is not necessarily required. Examples of the binding resin include thermoplastic resins such as styrene polymer, styrene-butadiene copolymer, styrene-acrilonitrile copolymer, styrene-maleic acid copolymer, acrylic polymer, styrene-acrylic copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfon, diaryl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, etc.; crosslinking thermosetting resins such as silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, etc.; photosetting resins such as epoxy-acrylate, urethane-acrylate, etc. These binding resins can be used alone or in combination thereof. Additives such as sensitizers, fluorene compounds, antioxidants, ultraviolet absorbers, plasticizers, surfactants, leveling agents, etc. can be added to the photosensitive layer, in addition to the above respective components. In order to improve sensitivity of the electrophotosensitive material, there may be used sensitizers such as tert-phenyl, halonaphthoquinones, acenaphthylene, etc. in combination with the charge generating material. In the multi-layer electrophotosensitive material, the charge generating material constituting the charge generating layer and the binding resin can be used in various proportions. It is preferred that 5 to 1000 parts by weight, particularly 30 to 500 parts by weight of the charge generating material is used, based on 100 parts by weight of the binding resin. The charge transferring material constituting the charge transferring layer and the binding resin can be used in various proportions within such a range as not to prevent the transmission of the charge and as to prevent the crystallization of the charge transferring material. It is preferred that 10 to 500 parts by weight, particularly 25 to 200 parts by weight of the charge transferring material containing the benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f) as the hole transferring material is used, based on 100 parts by weight of the binding resin so as to easily transfer the charge generated in the charge generating layer due to light irradiation. Regarding the thickness of the multi-layer type photosensitive layer, it is preferred that the thickness of the charge generating layer is about 0.01 to 5 µm, particularly about 0.1 to 3 µm and the thickness of the charge transferring layer is about 2 to 100 µm, particularly about 5 to 50 µm. In the single-layer type electrophotosensitive material, it is suitable that 0.1 to 50 parts by weight, particularly 0.5 to 30 parts by weight of the charge generating material and 10 to 500 parts by weight, particularly 25 to 200 parts by weight of the hole transferring material containing the benzidine derivatives represented by the general formulas (1) and (1') and specific formulas (2-a) to (2-f) to (6) are used, based on 100 parts by weight of the binding resin. When using in combination with the electron transferring material, it is preferred to use the electron transferring material in the amount of 5 to 100 parts by weight, particularly 10 to 80 parts by weight, based on 100 parts by weight of the binding resin. It is preferred that the total amount of the hole transferring and electron transferring materials is 20 to 500 parts by weight, particularly 30 to 200 parts, based on 100 parts by weight of the binding resin. A barrier layer (undercoat layer) may be formed, in such a range as not to injure the characteristics of the electrophotosensitive material, between the conductive substrate and the photosensitive layer in the single-layer type electrophotosensitive material, or between the conductive substrate and the charge generating layer, between the conductive substrate and the charge transferring layer or between the charge generating layer and the charge transferring layer in the multi-layer type electrophotosensitive material. Further, a protective layer may be formed on the surface of the electrophotosensitive material. As the conductive substrate on which the above respective layers are formed, various materials having conductivity can be used, and examples thereof include metals such as aluminum, copper, tin, platinum, silver, iron, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, etc.; plastic materials vapor-deposited or laminated with the above metal; glass materials coated with aluminum iodide, tin oxide, indium oxide, etc. The conductive substrate may be made in the form of a sheet or a drum. The substrate itself may have conductivity or only the surface of the substrate may have conductivity. It is preferred that the conductive substrate has a sufficient mechanical strength when used. When the above respective layers constituting the electrophotosensitive material are formed by a coating method, the charge generating material, the charge transferring material, the binding resin, etc. may be dispersed/mixed with a suitable solvent by a known method, for example, using a roll mill, a ball mill, an atriter, a paint shaker, a supersonic dispenser, etc. to prepare a coating solution, which is applied by a known means and then allowed to dry. As the solvent for preparing the coating solution, there can be used various organic solvents, and examples thereof include alcohols such as methanol, ethanol, isopropanol, butanol, etc.; aliphatic hydrocarbons such as n-hexane, octane, cyclohexane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, etc.; halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene, etc.; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, etc.; esters such as ethyl acetate, methyl acetate, etc.; dimethylformaldehyde, dimethylformamide, dimethylsulfoxide, etc. These solvents may be used alone or in combination thereof. In order to improve dispersibility of the charge transferring material and charge generating material as well as smoothness of the surface of the photosensitive layer, there may be used surfactants, leveling agents, etc. As described above, the benzidine derivative of the present invention has excellent compatibility with the binding resin while maintaining high hole transferring capability, and has a high melting point in comparison with a conventional benzidine derivative. Therefore, when it is dispersed in the binding resin, the glass transition temperature of the obtained membrane can become higher, thereby improving durability, heat resistance, etc. of the membrane. Accordingly, the benzidine derivative of the present invention can be suitably used as a hole transferring material in applications such as solar battery, electroluminescent device, electrophotosensitive material and the like. Further, the electrophotosensitive material of the present invention has high sensitivity and is superior in durability and heat resistance. EXAMPLES The following Synthesis Examples, Examples and Comparative Examples further illustrate the present invention in detail. Synthesis Example 1 14.8 g of N,N'-diacetyl-3,3'-dimethylbenzidine, 23.2 g of 3,4-dimethyliodobenzene, 13.8 g of potassium carbonate and 1 g of copper powder were added in 150 ml of nitrobenzene, and the mixture was refluxed with vigorous stirring while a nitrogen gas was bubbling into this reaction system for 24 hours. The water produced in the reaction was removed out of the reaction system by azeotropic distillation with nitrobenzene. After the reaction solution was cooled, the inorganic substance was filtered off. Further, nitrobenzen was distilled off by steam distillation to give the residue, which was dissolved in 100 ml of tetrahydrofuran together with 10 % hydrochloric acid. The solution was deacetylated under reflux for 2 hours to give N,N'-bis(3,4-dimethylphenyl)-3,3'-dimethylbenzidine. Then, 10.5 g of N,N'-bis(3,4-dimethylphenyl)-3,3'-dimethylbenzidine, 13.0 g of 4-n-butyliodobenzene, 13.8 g of potassium carbonate and 1 g of copper powder were added in 150 ml of nitrobenzene, and the mixture was refluxed with vigorous stirring while a nitrogen gas was blowing into this reaction system for 24 hours. The water produced in the reaction was removed out of the reaction system by azeotropic distillation with nitrobenzene, similar to the above case. After the reaction solution was cooled, the inorganic substance was filtered off. Further, nitrobenzen was distilled off by steam distillation to give the residue, which was dissolved in 100 ml of cyclohexane and the solution was purified by subjecting to silica gel chromatography and cyclohexane was distilled off to give a white precipitation. Then, the white precipitation was recrystallized from n-hexane to give N,N'-bis(3,4-dimethylphenyl)-N,N'-bis(n-butylphenyl)-3,3'-dimethylbenzidine of the above formula (1-a) as an objective product (8.7 g, yield: 27.3 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 1. Elemental analysis (%), Calcd.: C, 87.65; H, 8.26; N, 4.09 Found: C, 87.60; H, 8.24; N, 4.14 Melting point: 180.6 °C Synthesis Example 2 According to the same manner as that described in Synthesis Example 1 except for using 23.2 g of 2,4-dimethyliodobenzene in place of 3,4-dimethyliodobenzene and using 12.3 g of 4-isopropyliodobenzene in place of 4-n-butyliodobenzene, N,N'-bis(2,4-dimethylphenyl)-N,N'-bis(4-isopropylphenyl)-3,3'-dimethylbenzidine of the above formula (1-b) was obtained (8.4 g, yield:27.2 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 2. Elemental analysis (%), Calcd.: C, 87.47; H, 7.99; N, 4.26 Found: C, 87.70; H, 7.97; N, 4.31 Melting point: 182.6 °C Synthesis Example 3 According to the same manner as that described in Synthesis Example 1, a compound of the above formula (1-c) was obtained using a suitable starting material. Melting point: 181.9 °C Synthesis Example 4 20.3 G of 4,4'-diiodobiphenyl, 21.3 g of p-isopropylacetanilide, 13.8 g of potassium carbonate and 1 g of copper powder were added in 150 ml of nitrobenzene, and the mixture was refluxed with vigorous stirring while a nitrogen gas was bubbling into this reaction system for 24 hours. The water produced in the reaction was removed out of the reaction system by azeotropic distillation with nitrobenzene. After the reaction solution was cooled, the inorganic substance was filtered off. Further, nitrobenzen was distilled off by steam distillation to give the residue, which was dissolved in 100 ml of tetrahydrofuran together with 10 % hydrochloric acid. The solution was refluxed for 2 hours to give N,N'-bis(4-isopropylphenyl)benzidine. Then, 10.5 g of N,N'-bis(4-isopropylphenyl)benzidine, 11.6 g of 2,4-dimethyliodobenzene, 13.8 g of potassium carbonate and 1 g of copper powder were added in 150 ml of nitrobenzene, and the mixture was refluxed with vigorous stirring while a nitrogen gas was bubbling into this reaction system for 24 hours. The water produced in the reaction was removed out of the reaction system by azeotropic distillation with nitrobenzene, similar to the above case. After the reaction solution was cooled, the inorganic substance was filtered off. Further, nitrobenzen was distilled off by steam distillation to give the residue, which was dissolved in cyclohexane and the solution was purified by subjecting to silica gel chromatography and cyclohexane was distilled off to give a white precipitation. Then, the white precipitation was recrystallized from n-hexane to give N,N'-bis(2,4-dimethylphenyl)-N,N'-bis(4-isopropylphenyl)benzidine of the above formula (1-d) (8.3 g, yield: 29.0 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 3. Elemental analysis (%), Calcd.: C, 87.84; H, 7.71; N, 4.45 Found: C, 87.83; H, 7.66; N, 4.50 Melting point: 187.6 °C Synthesis Examples 5 and 6 According to the same manner as that described in Synthesis Example 4, compounds of the formulas (1-e) and (1-f) were obtained, respectively, using a suitable starting material. Melting point of the compound of the formula (1-e): 185.4 °C Melting point of the compound of the formula (1-f): 183.9 °C Synthesis Example 7 According to the same manner as that described in Synthesis Example 1, 14.8 g of N,N'-diacetyl-3,3'-diethylbenzidine was reacted with 23.2 g of 2,4-dimethyliodobenzene to give N,N'-bis(2,4-dimethylphenyl)-3,3'-dimethylbenzidine. According to the same manner as that described in Synthesis Example 1, 10.5 g of N,N'-bis(2,4-dimethylphenyl)-3,3'-dimethylbenzidine was reacted with 15.4 g of 4-ethyl-4'-iodophenyl to give N,N'-bis(2,4-dimethylphenyl)-N,N'-bis(4'-ethylbiphenyl-4-yl)-3,3'-dimethylbenzidine of the above formula (1-g) (7.8 g, yield: 21.3 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 4. Elemental analysis (%), Calcd.: C, 89.17; H, 7.24; N, 3.59 Found: C, 88.98; H, 7.22; N, 3.78 Melting point: 204.4 °C Synthesis Example 8 According to the same manner as that described in Synthesis Example 7 except for using 23.2 g of 3,4-dimethyliodobenzene in place of 2,4-dimethyliodobenzene to give N,N'-bis(3,4-dimethylphenyl)-N,N'-bis(4'-ethylbiphenyl-4-yl)-3,3'-dimethylbenzidine of the above formula (1-h) (7.9 g, yield: 22.1 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 5. Elemental analysis (%), Calcd.: C, 89.17; H, 7.24; N, 3.59 Found: C, 88.94; H, 7.21; N, 3.83 Melting point: 236.3 °C Synthesis Examples 9 and 10 According to the same manner as that described in Synthesis Example 7, compounds of the formulas (1-i) and (1-j) were obtained, respectively, using a suitable starting material. Melting point of the compound of the formula (1-i): 218.4 °C Melting point of the compound of the formula (1-j): 237.2 °C Examples 1 to 10 and Comparative Examples 1 to 7 (Single-layer type electrophotosensitive material for digital light source) 5 Parts by weight of X-type metal-free phthalocyanine as the charge generating material, 50 parts by weight of a benzidine derivative as the hole transferring material (HTM), 30 parts by weight of 3,5-dimethyl-3',5'-di-tert-butyldiphenoquinone of the formula (12): as the electron transferring material and 100 parts by weight of polycarbonate as the binding resin were mixed/dispersed with 800 parts by weight of tetrahydrofuran using a ball mill for 50 hours to prepare a coating solution for single-layer type photosensitive layer. Then, this coating solution was applied on an aluminum tube as the conductive substrate by a dip coating method, followed by hot-air drying at 100 °C for 60 minutes to give a single-layer type electrophotosensitive material for digital light source which has a single-layer type photosensitive layer of 15 to 20 µm in film thickness. The respective compounds of the benzidine derivative used in Examples 1 to 10 are shown by the number of the compounds in Table 1. Further, the respective benzidine derivatives of the numbers (13) to (19) used in Comparative Examples 1 to 7 are the following compounds. The melting point of benzidine derivatives (13) to (19) used in the respective Comparative Examples are shown below, respectively. (Number of compound) (Melting point) (13) 171.0 °C (14) 195.2 °C (15) 201.2 °C (16) 194.3 °C (17) 193.5 °C (18) 170.1 °C (19) 135.6 °C The following tests were conducted as to the electrophotosensitive materials of the above Examples and Comparative Examples, and their characteristics were evaluated. Initial electrical characteristics test (I) By using a drum sensitivity tester manufactured by GENTEC Co., a voltage was applied on the surface of an electrophotosensitive material to charge the surface at +700 V. Then, monochromatic light having a wavelength of 780 nm (half-width: 20 nm) and a light intensity of 16 µW/cm 2 from white light of a halogen lamp as an exposure light source through a band-pass filter was irradiated on the surface of the electrophotosensitive material for 80 msec. (irradiation time) and the time which is necessary for the above surface potential to be reduced to half, i.e. +350 V was measured, thereby calculating a half-life exposure E 1/2 (µJ/cm 2 ). Further, a surface potential at the time at which 330 msec. has passed since the beginning of exposure was measured as a potential after exposure V L (V). Measurement of glass transition temperature A photosensitive layer (about 5 mg) was peeled off from an electrophotosensitive material and the photosensitive layer was placed in an exclusive aluminum pan, which was sealed to prepare a sample to be measured. Then, the measurement was conducted as to the sample under the following conditions using a differential scanning calorimeter (type DSC8230D, manufactured by Rigaku Denki Co., Ltd.). An extrapolation glass transition temperature (Tig) of the sample was determined from the measurement results according to a "method for measuring a transition temperature of a plastic" defined in JIS K 7121. Atmospheric gas: air Heating rate: 20 °C/minute High-temperature resistance test An electrophotosensitive material was attached to an imaging unit of a facsimile for normal paper (type LDC-650, manufactured by Mita Industrial Co., Ltd.) and stored at an atmospheric temperature of 50 °C for 10 days at a state where a cleaning blade was always pressure-contacted on the surface of the electrophotosensitive material at a linear pressure of 1.5 g/mm. Then, a state of the surface of the photosensitive layer was measured with an utility surface profile-measuring apparatus (type SE-3H, manufactured by Kosaka Kenkyusho Co., Ltd.) and a maximum depth of the resulting dent was recorded. In the following tables, the description "<0.3 µm" in the column of the dent means that no dent was observed at all because the surface roughness of a normal electrophotosensitive material having no dent is about 0.5 µ. The results are shown in Table 1. HTM V L (V) E 1/2 (µJ/cm 2 ) Tig (°C) Dent (µm) Example 1 1-a 177 0.71 73.2 < 0.3 Example 2 1-b 170 0.68 72.1 < 0.3 Example 3 1-c 174 0.71 72.4 < 0.3 Example 4 1-d 162 0.68 73.5 < 0.3 Example 5 1-e 164 0.69 72.9 < 0.3 Example 6 1-f 166 0.68 72.5 < 0.3 Example 7 1-g 175 0.71 74.4 < 0.3 Example 8 1-h 179 0.71 74.7 < 0.3 Example 9 1-i 182 0.73 75.0 < 0.3 Example 10 1-j 184 0.72 75.2 < 0.3 Comp. Example 1 (13) 218 0.90 65.3 1.8 Comp. Example 2 (14) 215 0.90 72.7 < 0.3 Comp. Example 3 (15) 207 0.85 73.9 < 0.3 Comp. Example 4 (16) 210 0.85 73.0 < 0.3 Comp. Example 5 (17) 212 0.87 73.1 < 0.3 Comp. Example 6 (18) 245 1.17 65.6 1.6 Comp. Example 7 (19) 178 0.70 68.4 1.1 As apparent from Table 1, all of the electrophotosensitive materials of the respective Comparative Example using a conventional benzidine derivative were inferior in durability and heat resistance because their extrapolation glass transition temperature (Tig) was low and large dent was observed in the high-temperature resistance test. To the contrary, all of the electrophotosensitive materials of the respective Examples were superior in durability and heat resistance because their extrapolation glass transition temperature (Tig) was high and no dent was observed in the high-temperature resistance test, as well as their small half-life exposure E 1/2 (µJ/cm 2 ) and low potential after exposure V L (V). Examples 11 to 40 and Comparative Examples 8 to 31 (Single-layer type electrophotosensitive material for analogue light source) 5 Parts by weight of any one of azo pigments represented by the formulas: as the charge generating material (CGM), 70 parts by weight of a benzidine derivative as the hole transferring material (HTM), 20 parts by weight of 3,5-dimethyl-3',5'-di-tert-butyldiphenoquinone of the above formula (12) as the electron transferring material and 100 parts by weight of polycarbonate as the binding resin were mixed/dispersed with 800 parts by weight of tetrahydrofuran using a ball mill for 50 hours to prepare a coating solution for single-layer type photosensitive layer. Then, this coating solution was applied on an aluminum tube as the conductive substrate by a dip coating method, followed by hot-air drying at 100 °C for 60 minutes to give a single-layer type electrophotosensitive material for analogue light source which has a single-layer type photosensitive layer of 15 to 20 µm in film thickness. The respective benzidine derivatives used in the above Examples and Comparative Examples are shown by the number of the compounds described above. The following initial electrical characteristics test (II) was conducted as to the respective single-layer type electrophotosensitive materials thus obtained, and their characteristics were evaluated. Initial electrical characteristics test (II) By using a drum sensitivity tester manufactured by GENTEC Co., a voltage was applied on the surface of an electrophotosensitive material to charge the surface at +700 V. Then, white light (light intensity: 147 µW/cm 2 ) of a halogen lamp as an exposure light was irradiated on the surface of the electrophotosensitive material for 50 msec. (irradiation time) and the time which is necessary for the above surface potential to be reduced to half, i.e. +350 V was measured, thereby calculating a half-life exposure E 1/2 (µJ/cm 2 ). Further, a surface potential at the time at which 330 msec. has passed since the beginning of exposure was measured as a potential after exposure V L (V). The above results are shown in Tables 2 to 4. In Table 4, the test results of glass transition temperature and high-temperature resistance measured according to the same manner as mentioned above are also shown. HTM CGM V L (V) E 1/2 (µJ/cm 2 ) Example 11 1-a CG-1 182 3.65 Example 12 1-b CG-1 179 3.60 Example 13 1-c CG-1 182 3.69 Comp. Example 8 (13) CG-1 202 4.25 Comp. Example 9 (14) CG-1 204 4.25 Comp. Example 10 (15) CG-1 199 3.99 Example 14 1-a CG-2 184 3.69 Example 15 1-b CG-2 180 3.61 Example 16 1-c CG-2 181 3.59 Comp. Example 11 (13) CG-2 210 4.32 Comp. Example 12 (14) CG-2 213 4.33 Comp. Example 13 (15) CG-2 207 4.40 Example 17 1-a CG-3 186 3.67 Example 18 1-b CG-3 182 3.64 Example 19 1-c CG-3 180 3.66 Comp. Example 14 (13) CG-3 220 4.41 Comp. Example 15 (14) CG-3 221 4.38 Comp. Example 16 (15) CG-3 219 4.35 HTM CGM V L (V) E 1/2 (µJ/cm 2 ) Example 20 1-d CG-1 182 3.69 Example 21 1-e CG-1 185 3.78 Example 22 1-f CG-1 184 3.74 Comp. Example 8 (13) CG-1 202 4.25 Comp. Example 17 (16) CG-1 206 4.27 Comp. Example 18 (14) CG-1 204 4.25 Comp. Example 19 (17) CG-1 209 4.30 Example 23 1-d CG-2 175 3.63 Example 24 1-e CG-2 179 3.69 Example 25 1-f CG-2 181 3.71 Comp. Example 11 (13) CG-2 210 3.32 Comp. Example 20 (16) CG-2 207 4.40 Comp. Example 21 (14) CG-2 213 4.33 Comp. Example 22 (17) CG-2 214 4.34 Example 26 1-d CG-3 183 3.70 Example 27 1-e CG-3 184 3.68 Example 28 1-f CG-3 180 3.69 Comp. Example 14 (13) CG-3 220 4.41 Comp. Example 23 (16) CG-3 219 4.35 Comp. Example 24 (14) CG-3 221 4.38 Comp. Example 25 (17) CG-3 220 4.39 HTM CGM V L (V) E 1/2 (µJ/cm 2 ) Tig (°C) Dent (µm) Example 29 1-g CG-1 150 3.22 71.4 <0.3 Example 30 1-h CG-1 149 3.20 72.0 <0.3 Example 31 1-i CG-1 157 3.30 71.3 <0.3 Example 32 1-j CG-1 159 3.29 70.9 <0.3 Comp. Example 8 (13) CG-1 202 4.25 - - Comp. Example 26 (18) CG-1 237 5.63 - - Comp. Example 27 (19) CG-1 152 3.24 66.7 1.5 Example 33 1-g CG-2 158 3.30 70.9 <0.3 Example 34 1-h CG-2 151 3.20 72.2 <0.3 Example 35 1-i CG-2 155 3.22 71.8 <0.3 Example 36 1-j CG-2 159 3.29 70.5 <0.3 Comp. Example 11 (13) CG-2 210 4.32 - - Comp. Example 28 (18) CG-2 240 5.63 - - Comp. Example 29 (19) CG-2 154 3.21 65.9 1.4 Example 37 1-g CG-3 160 3.33 72.0 <0.3 Example 38 1-h CG-3 155 3.25 71.1 <0.3 Example 39 1-i CG-3 152 3.21 70.7 <0.3 Example 40 1-j CG-3 159 3.27 71 5 <0.3 Comp. Example 14 (13) CG-3 220 4.41 - - Comp. Example 30 (18) CG-3 239 5.64 - - Comp. Example 31 (19) CG-3 156 3.23 66.2 1.6 As apparent from Tables 2 to 4, all of the electrophotosensitive materials of the Examples were superior in sensitivity because of their small half-life exposure E 1/2 (µJ/cm 2 ) and low potential after exposure V L (V). From Table 4, it is recognized that all of the electrophotosensitive materials of the respective Examples were superior in durability and heat resistance because their extrapolation glass transition temperature (Tig) was high and no dent was observed in the high-temperature resistance test. Examples 41 to 46 (Multi-layer type electrophotosensitive material for digital light source) 2 Parts by weight of X-type metal-free phthalocyanine as the charge generating material and 1 part of polyvinyl butyral as the binding resin were mixed/dispersed with 120 parts by weight of dichloromethane using a ball mill for 50 hours to prepare a coating solution for charge generating layer. Then, this coating solution was applied on an aluminum tube by a dip coating method, followed by hot-air drying at 100 °C for 60 minutes to form a charge generating layer of 0.5 µm in film thickness. Then, 80 parts by weight of a benzidine derivative as the hole transferring material and 100 part of polycarbonate as the binding resin were mixed/dispersed with 800 parts by weight of benzene using a ball mill for 50 hours to prepare a coating solution for charge transferring layer. Then, this coating solution was applied on the above charge generating layer by a dip coating method, followed by hot-air drying at 90 °C for 60 minutes to form a charge transferring layer of 15 µm in film thickness, thereby producing a multi-layer type electrophotosensitive material for digital light source. The following initial electrical characteristics test (III) was conducted as to the respective multi-layer type electrophotosensitive materials thus obtained, and their characteristics were evaluated. Initial electrical characteristics test (III) By using a drum sensitivity tester manufactured by GENTEC Co., a voltage was applied on the surface of the electrophotosensitive materials of the Examples to charge the surface at -700 V. Then, monochromatic light having a wavelength of 780 nm (half-width: 20 nm) and a light intensity of 16 µW/cm 2 from white light of a halogen lamp as an exposure light source through a band-pass filter was irradiated on the surface of the electrophotosensitive material for 50 msec. (irradiation time) and the time which is necessary for the above surface potential to be reduced to half, i.e. -350 V was measured, thereby calculating a half-life exposure E 1/2 (µJ/cm 2 ). Further, a surface potential at the time at which 330 msec. has passed since the beginning of exposure was measured as a potential after exposure V L (V). The results are shown in Table 5. HTM V L (V) E 1/2 (µJ/cm 2 ) Example 41 1-a -129 0.59 Example 42 1-b -124 0.56 Example 43 1-g -127 0.58 Example 44 1-h -130 0.59 Example 45 1-d -122 0.51 Example 46 1-e -124 0.53 As is apparent from Table 5, all of the electrophotosensitive materials of the respective Examples were superior in sensitivity because of their small half-life exposure E 1/2 (µJ/cm 2 ) and low potential after exposure V L (V). Synthesis Example 11 10.6 G of 3,3'-dimethylbenzidine, 46.4 g of 2,4-dimethyliodobenzene, 27.6 g of potassium carbonate and 2 g of copper powder were added in 150 ml of nitrobenzene, and the mixture was refluxed with vigorous stirring while a nitrogen gas was bubbling into this reaction system for 24 hours. The water produced in the reaction was removed out of the reaction system by azeotropic distillation with nitrobenzene. After the reaction solution was cooled, the inorganic substance was filtered off. Further, nitrobenzen was distilled off by steam distillation to give the residue, which was dissolved in cyclohexane and the solution was purified by subjecting to silica gel chromatography and cyclohexane was distilled off to give a white precipitation. Then, the white precipitation was recrystallized from n-hexane to give N,N, N',N'-tetrakis(2,4-dimethylphenyl)-3,3'-dimethylbenzidine of the above formula (2-a) (13.24 g, yield: 42.1 %). The results of the infrared spectroscopic analysis of the resulting product are shown in Fig. 6 Elemental analysis (%), Calcd.: C, 87.65; H, 7.69; N, 4.45 Found: C, 87.76; H, 7.81; N, 4.43 Melting point: 239.9 °C Synthesis Examples 12 to 16 According to the same manner as that described in Synthesis Example 11, compounds of the formulas (2-b) to (2-f) were obtained, respectively, using a suitable starting material. (Number of compound) (Melting point) (2-b) 210.3 °C (2-c) 201.4 °C (2-d) 217.8 °C (2-e) 210.0 °C (2-f) 199.2 °C Examples 47 to 49 and Comparative Examples 32 to 37 (Electrophotosensitive material for digital light source) According to the same manner as that described in Example 1 except for using a benzidine derivative shown by the number of the compound in Table 6 as the hole transferring material (HTM), an electrophotosensitive material for digital light source which has a single-layer type photosensitive layer of 15 to 20 µm in film thickness was produced. The benzidine derivatives of the numbers (20) to (25) used in Comparative Examples 32 to 37 are the following compounds. The melting point of benzidine derivatives (20) to (25) are shown below, respectively. (Number of compound) (Melting point) (20) 220.1 °C (21) 219.7 °C (22) 204.2 °C (23) 195.9 °C (24) 203.3 °C (25) 201.0 °C According to the same manner as that described in Example 1, the resulting electrophotosensitive materials were subjected to the initial electrical characteristics test (I), the measurement of glass transition temperature and the high-temperature resistance test. The results are shown in Table 6. HTM V L (V) E 1/2 (µJ/cm 2 ) Tig (°C) Dent (µm) Example 47 2-a 210 0.88 75.0 < 0.3 Example 48 2-c 215 0.90 72.7 < 0.3 Example 49 2-d 204 0.83 74.2 < 0.3 Comp. Example 1 (13) 218 0.90 65.3 1.8 Comp. Example 32 (20) 239 1.24 74.6 < 0.3 Comp. Example 33 (21) 231 1.08 74.5 < 0.3 Comp. Example 34 (22) 244 1.44 73.6 < 0.3 Comp. Example 35 (23) 230 1.15 72.9 < 0.3 Comp. Example 36 (24) 243 1.42 73.4 < 0.3 Comp. Example 37 (25) 233 1.11 73.2 < 0.3 Examples 50 to 58 and Comparative Examples 38 to 55 (Electrophotosensitive material for analogue light source) According to the same manner as that described in Example 11 except for using a benzidine derivative described in Tables 7 and 8 as the hole transferring material, a single-layer type electrophotosensitive material for analogue light source was produced. The resulting electrophotosensitive materials were subjected to the same initial electrical characteristics test (II) as that of Example 11, and their characteristics were evaluated. The results are shown in Tables 7 and 8. HTM CGM V L (V) E 1/2 (µJ/cm 2 ) Example 50 2-a CG-1 200 4.02 Example 51 2-c CG-1 204 4.25 Example 52 2-d CG-1 194 3.95 Comp. Example 8 (13) CG-1 202 4.25 Comp. Example 38 (20) CG-1 236 4.48 Comp. Example 39 (21) CG-1 224 4.39 Comp. Example 40 (22) CG-1 237 4.53 Comp. Example 41 (23) CG-1 222 4.36 Comp. Example 42 (24) CG-1 241 4.55 Comp. Example 43 (25) CG-1 227 4.40 Example 53 2-a CG-2 201 4.03 Example 54 2-c CG-2 199 4.00 Example 55 2-d CG-2 197 3.98 Comp. Example 11 (13) CG-2 210 4.32 Comp. Example 44 (20) CG-2 245 4.58 Comp. Example 45 (21) CG-2 239 4.50 Comp. Example 46 (22) CG-2 238 4.47 Comp. Example 47 (23) CG-2 230 4.45 Comp. Example 48 (24) CG-2 249 4.61 Comp. Example 49 (25) CG-2 232 4.52 HTM CGM V L (V) E 1/2 (µJ/cm 2 ) Example 56 2-a CG-3 204 4.19 Example 57 2-c CG-3 206 4.24 Example 58 2-d CG-3 200 4.20 Comp. Example 14 (13) CG-3 220 4.41 Comp. Example 50 (20) CG-3 250 4.62 Comp. Example 51 (21) CG-3 241 4.56 Comp. Example 52 (22) CG-3 260 4.68 Comp. Example 53 (23) CG-3 233 4.44 Comp. Example 54 (24) CG-3 259 4.70 Comp. Example 55 (25) CG-3 239 4.52

Claims: A benzidine derivative represented by the general formula (1): wherein R 1 and R 2 are the same or different and indicate a hydrogen atom or a methyl group; R 3 and R 4 indicate a methyl group; R 5 and R 6 are the same or different and indicate an alkyl group having 3 to 5 carbon atoms or a phenyl group which may contain a substituent; and m and n are the same or different and indicate an integer of 2 or 3. A benzidine derivative according to claim 1, which is represented by the general formula (1'): wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , m and n are as defined in claim 1. A benzidine derivative represented by any one of the formulae (2-a) to (2-f): An electrophotosensitive material comprising a conductive substrate, and a photosensitive layer provided on the conductive substrate, said photosensitive layer containing the benzidine derivative represented by the general formula (1) of claim 1, the general formula (1') of claim 2, and any of the formulae (2-a) to (2-f) of claim 3,

Inventors: FUKAMI TOSHIYUKI, KAKUI MIKIO, MIZUTA YASUFUMI, MUTO NARIAKI, NAKAMORI HIDEO, SAITO SAKAE, SHIOMI HIROSHI, SUMIDA KEISUKE, TANAKA MASASHI, UCHIDA MAKI, FUKAMI, TOSHIYUKI, KAKUI, MIKIO, MIZUTA, YASUFUMI, MUTO, NARIAKI, NAKAMORI, HIDEO, SAITO, SAKAE, SHIOMI, HIROSHI, SUMIDA, KEISUKE, TANAKA, MASASHI, UCHIDA, MAKI, FUKAMI, TOSHIYUKI, C/O MITA INDUSTRIAL CO.,LTD., KAKUI, MIKIO, C/O MITA INDUSTRIAL CO.,LTD., MIZUTA, YASUFUMI, C/O MITA INDUSTRIAL CO.,LTD., MUTO, NARIAKI, C/O MITA INDUSTRIAL CO.,LTD., NAKAMORI, HIDEO, C/O MITA INDUSTRIAL CO.,LTD., SAITO, SAKAE, C/O MITA INDUSTRIAL CO.,LTD., SHIOMI, HIROSHI, C/O MITA INDUSTRIAL CO.,LTD., SUMIDA, KEISUKE, C/O MITA INDUSTRIAL CO.,LTD., TANAKA, MASASHI, C/O MITA INDUSTRIAL CO.,LTD., UCHIDA, MAKI, C/O MITA INDUSTRIAL CO.,LTD.
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1994
Main classification: C07C211
IPC codes: G03G5, C07C211